This invention relates to a device for measuring quantities of heat while simultaneously measuring the evaporation kinetics and/or condensation kinetics of most minute amounts of liquid in order to determine thermodynamic parameters according to the species of patent claims. The quantities of heat can be absorbed during evaporation and/or released during condensation by very minute samples being mainly composed of liquid.
The inventive device predominantly serves to simultaneously measure the specific evaporation heat and vapor pressure of solutions at almost room temperature. Provided that a chemical equilibrium exists in the liquid and the evaporation process and/or condensation process are/is combined with a displacement of the chemical equilibrium, this device also serves to measure the specific chemical heat of reaction. For compound systems consisting of a solution being in contact with a solid (crystalline) phase of the solute, this device is used to measure the concentration of the saturated solution and the specific heat of solution, too. The most minute amount of liquid can also be a gel-like solvent-binding substance. The device is designated for measuring such kinds of solutions for which the vapor pressure of the solvent does not exceed the vapor pressure of the saturated water vapor in terms of magnitude and for which the vapor pressure of the solute above the solution has such a low value compared with the vapor pressure of the solvent that it can be ignored.
For all calorimeter principles to date the current state of art allows to derive the finding according to which the output that can still be measured becomes the smaller the faster the quantity of heat is released. The resulting characteristic time determines the minimum possible time constant required by the calorimeter to be able to measure the total quantity of heat released. Therefore, for maximum time constants of about 1000 s which are technically feasible today the output that can still be reliably measured is about 0.1 μW; it decreases down to about 10 nW for a time constant of 30 s. Consequently, the desired miniaturization of calorimeters for the application of very minute amounts of substances, e.g. when using thermally controlled micrometering cells based on chips, will only offer advantages for quantities of heat in the nJ range, if this quantity of heat is available within some seconds. This state-of-the-art finding is quite contrary to the demands placed on the measuring task to be solved by this inventive device.